放在凸透镜主光轴上焦点F以内的点光源S发出的光，通过凸透镜后的光路如图所示，则下列说法正确的是（   ）

下列结论不正确的是（   ）

食物链是根据动植物间（  ）的关系建立的。

    It seems to be strange to you there is a blind spot(点) on the eyes. Here is an interesting experiment that can make something disappear, when one eye is open.
　Make a card about the size of a postcard and write two English letters L and R on it, L on the left and R on the right. First, hold the card about 80 cm away and you see both the letters. Then close your right eye and look at the letter R only with your left eye. And now, as you move the card slowly towards you, you'll find the letter L disappearing. But if you move the card nearer to your face, the letter will be seen again. Now do the same experiment with your left eye closed, you'll find the letter R disappearing.
    Why does the letter disappear? It is because there is a blind spot on the eye. When the image of the letter falls on the blind spot, it won't be seen. That is why either of the letters disappears.

实验室制配0.5mol/L的NaOH溶液500mL，有以下仪器：①烧杯  ②100mL量筒  ③1000mL容量瓶  ④500mL容量瓶  ⑤玻璃棒  ⑥托盘天平（带砝码） ⑦滴定管